The present invention relates to attachments for rotary hand tools, and more specifically relates to alignment of attachments to rotary hand tools.
Small rotary hand tools that have a generally cylindrical housing or case have been marketed for many years for use in carrying out various woodworking and metal working tasks by hobbyists as well as commercial artisans. Such rotary hand tools generally have a motor unit with a rotary output shaft extending from the nose end and often have a nose portion that is configured to connect to various accessories or attachments. Some of these rotary hand tools are somewhat larger and more powerful and are known in the building trade as spiral saws that use a side cutting bit to penetrate and to rapidly cut holes for electrical outlets, light fixtures and switches and the like in dry wall. Because these tools are quite powerful even though they are relatively small, they are convenient to use on a jobsite or just about anywhere else where a source of AC power is available.
There has been continued innovation and improvement in the design of accessories for such hand tools, particularly with regard to the attachment of those accessories to a corresponding hand tool. Examples of those attachments are those produced under the Skil® and Bosch® brands by the Robert Bosch Tool Corporation of Mt. Prospect, Ill.
During use, it is important that accessories connecting directly to an output shaft of the rotary hand tool maintain a high level of alignment with respect to the motor output shaft axis, particularly where the rotational speed is high. However, conventional methods of coupling fail to provide sufficient precision alignment of the output axis of a rotary hand tool and the corresponding input axis of a rotary hand tool attachment, without simultaneously compromising the relative rigidity or tolerance of the coupling. Thus, during operation, misalignment frequently results in undesirable vibration. In addition, the heat generated from such vibration can eventually cause the attachment to weld itself to the rotary hand tool.